1. Field of the Invention
The field of this invention lies within the electronic art as it relates to the compensation of spurious signals on two relatively adjacent lines. More specifically, it relates to the utilization of a sense and a force line within a system in which the current in the sense line is to be read accurately and all spurious signals are to be nulled on the force and the sense line. It can be particularly applied to the solid state testing art as it relates to testers having lines connected to a device under test, such as an integrated circuit in which a voltage is to be forced and a current sensed therefrom.
2. The Prior Art
The prior art with regard to compensating for spurious signals in electronic lines has generally applied cross circuit connections, common modes, and certain regenerative types of compensation to avoid the incursion of spurious signals that might interfere with the desired signals on the lines.
Recently, it has been common to test various integrated circuits by means of an electronic tester. The tester is often controlled in part by a computer. The tester generates a signal that is provided to an integrated circuit, hereinafter referred to interchangeably as a device under test. The signal which oftentimes is a forced voltage or current, is provided to the device under test by various supply means that must be connected to the device through a switching network in the form of relays.
The connection lines tend to pick up spurious ambient signals, as well as a degree of dielectric absorption kickback when there are certain changes in voltage. The dielectric absorption kickback can be generated by changes of voltage either through switching of the relays, or changes in voltage dictated by the computer and provided by the tester.
The minimum requirements of a system for testing certain devices with a force and a sense line, is such that the entire system must be accurate on a static as well as a dynamic basis.
The prior art has not specifically solved the problem of currents generated by dielectric absorption kickback and spurious signals on adjacent lines by elimination thereof through shifting from a normal mode to a common mode. However, the inventor has found that the utilization of this principle at the current values on the force line with respect to its IR drop, enables the utilization of a common mode. In other words, the sense line can be placed in a position where it is free. Inasmuch as it runs along the same path as the force line, it normally picks up the same spurious current signals as the force line, so that it can be used to compensate for the spurious current signals within the system.
To effectuate the foregoing, the inputs are reversed so that a signal is generated 180.degree. out of phase with respect to the sense line and the force line. The force line and the sense line spurious current signals, by way of sixty cycle noise, other signal noises and dielectric absorption kickback, are nulled by the foregoing means. Stated another way, the output of an amplifier on the sense line is fed as the reference voltage to a current amplifier of the force line. The net result is that the inversion of the signal on the sense line when fed to the force line, nulls out the signals on the force line that have been spuriously created.
In effect, this invention provides an advance over the prior art by enabling a nulling of spurious current signals on a force and a sense line, or for that matter, all lines in adjacent relationship to each other. In particular, it is useful with regard to devices under test that are to be tested on a tester, wherein the forced voltages are transmitted and currents sensed from a remote location from the device under test.